This situation reminds me of a story I have heard about a meditation teacher who refused to removed an obnoxious student from his retreat center despite complaints from his other long time and loyal students about this man's behavior. When the students found out the teacher had actually begun paying him to attend, they were even more outraged. Eventually, the teacher explained that this man was providing very valuable lessons for all of them to practice equanimity, compassion, loving kindness and sympathetic joy which they were overlooking. Now, there is a difference between being obnoxious and being downright dangerous, however, the sensei may have something like this in his intentions. You still have the right to exercise the option of refusing to pair with this person. I would definitely excercise that option and hope that others in your dojo do the same. When a similar situation occurred in the dojo I train in, eventually the student left.

I highly recommend that you follow your gut-feeling anytime you are training with someone you feel is abusing you. (Or for that matter, even when you aren't training in the dojo.) If it feels like abuse, it is. When I began training, the sempai at the time paired with me and began doing some very rough things which I was not prepared to deal with since it was my first lesson. The first time, I said nothing, thinking I was just unaccustomed to being thrown around. The second time seemed to confirm my original opinion. When he did it a third time, I refused his hand to help me up, got up off the ground, dusted myself off and grabbed him by his shirt at his throat. I looked him in the eye and said, "Don't you ever do that to me again!". Of course, our sensei was aware of what was going on, but didn't interfere. I decided that if training meant I had to subject myself to abuse, then training in that dojo was not worth it. The sempai was in shock. He didn't know what to say or do, but he never tried it again. Eventually, he was demoted and left the dojo. But I learned a very valuable lesson about speaking up for myself which I never forgot.